1. Field of the Invention
The present invention relates to a movable-area covering mechanism for covering X-Y tables, etc.
2. Prior Art
Conventionally, in industrial machineries, such as semiconductor manufacturing apparatuses, two different types of tables are used: one is a table which moves uniaxially (or in the X or Y direction only) and the other is a table which moves biaxially (or in both the X and Y directions). For these tables, covers are used so as to cover the area wherein the tables are moved, thus avoiding dust from the table moving areas, securing a safety, and improving the appearance of the table, etc.
Several different types of movable-area covering mechanisms are know presently. These are shown in FIGS. 4 through 7.
FIG. 4 illustrates a bellows type covering system. One end of a bellows 40 is fastened to a fixed cover 1, and the other end to a movable member 4 which is secured to the table.
FIG. 5 shows a single-plate type cover. A covering plate 41 is fastened to a movable member 4 so that the covering plate 41 covers the opening 1a of the fixed cover 1.
In FIG. 6, a stacked-plate type covering system is illustrated. In this covering system, a multiple number of covering plates 42, 43 and 44 are placed one on the other and fit over a movable member 4. These covering plates are mounted on the surface of a fixed cover 1. Openings 42a, 43a and 44a are formed in the covering plates 42, 43 and 44 respectively, so that they are successively smaller than the opening 1a formed in the fixed cover 1.
FIG. 7 shows a skirt type covering system. In this system, one end of a skirt 45 is fastened to a fixed cover 1, while the other end of the skirt 45 is fastened to a movable member 4.
However, these conventional covering systems have problems.
In the bellows type system, the thickness C of the bellows 40, when contracted, is still large. Accordingly, it is impossible to install the bellows 40 in a small space. In addition, the stroke (distance) of the movable member 4 is small. If the stroke of the movable member 4 is large, then a larger space is required. Furthermore, this system tends to be expensive to manufacture, and trash, etc., are likely to accumulate in the valleys of the bellows 40. Thus, the dimension C increases as the stroke of the movable member 4 becomes longer.
In the case of single-plate type system of FIG. 5, a space is required for the entire stroke of the movable member 4; accordingly, it is impossible to install this mechanism in a small place.
In the stacked-plate type system shown in FIG. 6, several numbers of covering plates (more than three as shown in the Figure) are required as the opening 1a in the fixed cover 1 becomes larger. As a result, the covering plates generate more dirt when rubbed against each other. Furthermore, the manufacturing costs are high.
In the skirt type system shown in FIG. 7, the drooping skirt part 45a is easily entangled with the movable member 4 when the movable member 4 moves to one end of the opening 1a.